Methods and apparatus for processing a substrate

ABSTRACT

Methods and apparatus for processing a substrate are provided herein. For example, a method for processing a substrate includes applying at least one of low frequency RF power or DC power to an upper electrode formed from a high secondary electron emission coefficient material disposed adjacent to a process volume; generating a plasma comprising ions in the process volume; bombarding the upper electrode with the ions to cause the upper electrode to emit electrons and form an electron beam; and applying a bias power comprising at least one of low frequency RF power or high frequency RF power to a lower electrode disposed in the process volume to accelerate electrons of the electron beam toward the lower electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 16/668,107, which was filed on Oct. 30, 2019, theentire contents of which is incorporated herein by reference.

FIELD

Embodiments of the present disclosure generally relate to methods andapparatus for processing a substrate, and more particularly, to methodsand apparatus configured for electron beam reactive plasma etching of asubstrate.

BACKGROUND

In accordance with current substrate (e.g., wafer) manufacture, etchspeed, etch profile, and etch selectivity can be controlled to lowermanufacturing cost and increase circuit element density on a substrate.Etch features (e.g., memory holes, slits, etc.) on a substrate, however,continue to shrink in size or increase in aspect ratio (e.g., ratio ofdepth to width of a feature). For example, in three dimensional (3D)NAND device manufacture, substrates (wafers) can include up to 96 layersand can extend up to 128 layers. Additionally, an aspect ratio of amemory hole and/or slit, for example, can be between 100 to 200 with amemory hole depth ranging from about 6 μm to 8 μm, thus making memoryhole etching one of the most critical and challenging steps inmanufacture of 3D NAND devices. For example, such high aspect ratio(HAR) etching not only requires high etching speed and high etchingselectivity, e.g., to mask material on a substrate, but HAR etching alsorequires a straight profile without bowing and twisting, no under-etchand minimum micro-loading, minimum aspect ratio dependent etching(ARDE), and uniformity across the entire substrate (e.g., criticaldimension (CD) variation of 3σ<1%).

Likewise, for Finfet manufacture targeted for logic applications, thereis often a requirement to chemically etch similar materials with aselectivity ratio greater than 20, e.g., etch between silicon oxide andsilicon nitride).

Thus, the inventors have provided improved methods and apparatusconfigured for electron beam reactive plasma etching of a substrate.

SUMMARY

Methods and apparatus for electron beam reactive plasma etching of asubstrate are provided herein. In some embodiments, a method includesapplying at least one of low frequency RF power or DC power to an upperelectrode formed from a high secondary electron emission coefficientmaterial disposed adjacent to a process volume; generating a plasmacomprising ions in the process volume; bombarding the upper electrodewith the ions to cause the upper electrode to emit electrons and form anelectron beam; and applying a bias power comprising at least one of lowfrequency RF power or high frequency RF power to a lower electrodedisposed in the process volume to accelerate electrons of the electronbeam toward the lower electrode.

In accordance with one or more embodiments, an apparatus for processinga substrate includes a controller configured to: apply at least one oflow frequency RF power or DC power to an upper electrode formed from ahigh secondary electron emission coefficient material disposed adjacentto a process volume; generate a plasma comprising ions in the processvolume; and bombarding the upper electrode with the ions to cause theupper electrode to emit electrons and form an electron beam; and apply abias power comprising at least one of low frequency RF power or highfrequency RF power to a lower electrode disposed in the process volumeto accelerate electrons of the electron beam toward the lower electrode.

In accordance with one or more embodiments, a nontransitory computerreadable storage medium having stored thereon instructions that whenexecuted by a processor configure the processor to perform a method forprocessing a substrate. The method includes applying at least one of lowfrequency RF power or DC power to an upper electrode formed from a highsecondary electron emission coefficient material disposed adjacent to aprocess volume; generating a plasma comprising ions in the processvolume; bombarding the upper electrode with the ions to cause the upperelectrode to emit electrons and form an electron beam; and applying abias power comprising at least one of low frequency RF power or highfrequency RF power to a lower electrode disposed in the process volumeto accelerate electrons of the electron beam toward the lower electrode.

Other and further embodiments of the present disclosure are describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the disclosure depicted in the appendeddrawings. However, the appended drawings illustrate only typicalembodiments of the disclosure and are therefore not to be consideredlimiting of scope, for the disclosure may admit to other equallyeffective embodiments.

FIG. 1 is a schematic diagram of an apparatus, in accordance with one ormore embodiments of the present disclosure.

FIG. 2 is a flowchart of a method for processing a substrate, inaccordance with one or more embodiments of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. Elements and features of one embodiment may be beneficiallyincorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments of methods and apparatus configured for electron beamreactive plasma etching of a substrate are provided herein. Moreparticularly, in accordance with the present disclosure, the inventorshave found that when compared to conventional etching apparatus, e.g.,reactive ion etching (RIE), etching apparatus described herein: a)provide, for the same level of incident ion energy used by conventionaletching apparatus, increased etch rate, e.g., thirty percent increase inetch rate, b) provide increased source electron beam for increased etchrate without having to increase bias power, which conventional etchingapparatus sometime need increase to compensate for a reduction in ionenergy (e.g., caused by clogging), which can sometimes generate thermalload to a substrate (e.g., a wafer), c) eliminate micro-trenching, e.g.,due to charging effect which causes faster etching to occur in corner ofnon-flat etch fronts, d) provide increased etch depth while minimizingARDE effect, e.g., due to charging effect, and e) provide increasedprofile control, e.g., reduce, if not eliminate, bowing and/or twisting,due to charging effect at an upper portion of an etch feature.

FIG. 1 is a schematic diagram of an apparatus, in accordance with at oneor more embodiments of the present disclosure. The apparatus is suitablefor etching one or more substrates (wafers) using an electron beam(ebeam). Accordingly, in at least some embodiments, the apparatus is aprocess chamber 100 (e.g., an ebeam process chamber) that is configuredto perform ebeam induced etching (EBIE). The process chamber 100 has achamber body 102 which defines a process volume 101. In an embodiment,the chamber body 102 has a substantially cylindrical shape and may befabricated from a material suitable for maintaining a vacuum pressureenvironment therein, such as metallic materials, for example aluminum orstainless steel.

A ceiling 106 is coupled to the chamber body 102 and forms the processvolume 101. The ceiling 106 is formed from an electrically conductivematerial, such as the materials utilized to fabricate the chamber body102. The ceiling 106 is coupled to and supports an electrode 108 (e.g.,an upper electrode). In some embodiments, the electrode 108 is coupledto the ceiling 106 such that the electrode 108 is disposed adjacent orwithin the process volume 101. The electrode 108 is formed from aprocess-compatible material having a high secondary electron emissioncoefficient, e.g., a secondary electron emission coefficient, of about 5to about 10. Materials having relatively high secondary emissioncoefficients can include, but are not limited to, silicon, carbon,silicon carbon materials, or silicon-oxide materials. Alternatively, theelectrode 108 can be formed from a metal oxide material such as aluminumoxide (Al₂O₃), yttrium oxide (Y2O₃), or zirconium oxide (ZrO2). Adielectric ring 109, which is formed from an electrically insulatingmaterial, is coupled to the chamber body 102 and surrounds the electrode108. As illustrated, the dielectric ring 109 is disposed between thechamber body 102 and the ceiling 106 and supports the electrode 108.

The ceiling 106 can include an insulating layer 150 containing achucking electrode 152 facing the electrode 108. In at least someembodiments, a DC voltage power supply 154 can be coupled to thechucking electrode 152 via the feed conductor 155, for electrostaticallydamping the electrode 108 to the ceiling 106, and to the electrode 108for applying a DC power (e.g., a voltage potential) thereto. In suchembodiments, a DC blocking capacitor 156 can be connected in series withthe output of an impedance match circuit 124. A controller 126 functionsto control the DC voltage power supply 154.

Mechanical contact between the electrode 108 and the ceiling 106 issufficient to maintain high thermal conductance between the electrode108 and the ceiling 106. Additionally, a force of the mechanical contactcan be regulated by the electrostatic clamping force provided by the DCvoltage power supply 154.

In one or more embodiments, the ceiling 106 is electrically conductiveand in electrical contact with the electrode 108. Power from animpedance match circuit 124 is conducted through the ceiling 106 to theelectrode 108. In one or more embodiments, the chamber body 102 can bemaintained at ground potential. In one or more embodiments, groundedinternal surfaces (i.e., chamber body 102) inside the process chamber100 can be coated with a process compatible material such as silicon,carbon, silicon carbon materials, or silicon-oxide materials, aluminumoxide (Al₂O₃), yttrium oxide (Y₂O₃), or zirconium oxide (ZrO₂).

In some embodiments, internal passages (not shown) for conducting athermally conductive liquid or media inside the ceiling 106 areconnected to a thermal media circulation supply. The thermal mediacirculation supply acts as a heat sink or a heat source.

A pedestal 110 is disposed in the process volume 101. The pedestal 110supports a substrate 111 (e.g., semiconductor wafers, such as siliconwafers, or glass panels or other substrates, such as for solar cell,display, or other applications) thereon and has a substrate supportsurface 110 a oriented parallel to the electrode 108. In an embodiment,the pedestal 110 is movable in the axial direction by a lift servo 112.During operation, an upper electrode, such as the electrode 108, ismaintained at one or more distances (e.g., a process position) from thesubstrate support surface 110 a. For example, in at least someembodiments, the electrode 108 is maintained from a process position forprocessing a substrate at a distance from about 1 inch to about 20inches. For example, in at least some embodiments, the distance can beabout 6 inches to about 10 inches.

The controller 126 is provided and coupled to various components of theprocess chamber 100 to control the operation of the process chamber 100for processing a substrate. The controller 126 includes a centralprocessing unit (CPU) 127, support circuits 129 and a memory ornon-transitory computer readable storage medium 131. The controller 126is operably coupled to and controls one or more energy sources directly,or via computers (or controllers) associated with the process chamber100 and/or support system components. The controller 126 may be any formof general-purpose computer processor that can be used in an industrialsetting for controlling various chambers and sub-processors. The memory,or non-transitory computer readable storage medium, 131 of thecontroller 126 may be one or more of readily available memory such asrandom access memory (RAM), read only memory (ROM), floppy disk, harddisk, optical storage media (e.g., compact disc or digital video disc),flash drive, or any other form of digital storage, local or remote. Thesupport circuits 129 are coupled to the CPU 127 for supporting the CPU127 in a conventional manner. The support circuits 129 include cache,power supplies, clock circuits, input/output circuitry and subsystems,and the like. Inventive methods as described herein, such as the methodfor processing a substrate (e.g., EBIE of a substrate), may be stored inthe memory 131 as software routine 133 that may be executed or invokedto control the operation of the one or more energy sources in the mannerdescribed herein. The software routine 133 may also be stored and/orexecuted by a second CPU (not shown) that is remotely located from thehardware being controlled by the CPU 127.

In one or more embodiments, the pedestal 110 can include an insulatingpuck 142 which forms the substrate support surface 110 a, a lowerelectrode 144 disposed inside the insulating puck 142, and a chuckingvoltage supply 148 connected to the electrode 144. Additionally, in atleast some embodiments, a base layer 146 underlying the insulating puck142 can include one or more internal passages (not shown) forcirculating a thermal transfer medium (e.g., a liquid) from acirculation supply. In such embodiments, the circulation supply canfunction as a heat sink or as a heat source.

A high frequency RF power generator 120 having a frequency from about 20MHz to about 200 MHz and a low frequency RF power generator 122 having afrequency from about 100 kHz to about 20 MHz are coupled to theelectrode 108 through, for example, an impedance match circuit 124 viaan RF feed conductor 123. In one or more embodiments, the RF feedconductor 123 from the impedance match circuit 124 can be connected tothe electrode support or ceiling 106 rather than being directlyconnected to the electrode 108. In such embodiments, RF power from theRF feed conductor 123 can be capacitively coupled from the electrodesupport to the electrode 108. The impedance match circuit 124 is adaptedto provide an impedance match at the different frequencies of the highfrequency RF power generator 120 and the low frequency RF powergenerator 122, as well as filtering to isolate the high frequency RFpower generator 120 and the low frequency RF power generator 122 fromone another. Output power levels of the high frequency RF powergenerator 120 and the low frequency RF power generator 122 can beindependently controlled by a controller 126, as will be described ingreater detail below.

With the high frequency RF power generator 120 and the low frequency RFpower generator 122, radial plasma uniformity in the process volume 101can be controlled by selecting a distance (e.g., from about 6 inches toabout 10 inches) between the electrode 108 and pedestal 110. Forexample, in some embodiments, a lower VHF frequency produces anedge-high radial distribution of plasma ion density in the processvolume 101 and an upper VHF frequency produces a center-high radialdistribution of plasma ion density. With such a selection, the powerlevels of the high frequency RF power generator 120 and the lowfrequency RF power generator 122 are capable of generating a plasma witha substantially uniform radial plasma ion density.

Upper gas injectors 130 provide process gas into the process volume 101through a first valve 132, and lower gas injectors 134 provide processgas into the process volume 101 through a second valve 136. The uppergas injectors 130 and the lower gas injectors 134 can be disposed insidewalls of the chamber body 102. Process gas is supplied from an arrayof process gas supplies such as gas supplies 138 through an array ofvalves 140 which are coupled to the first valve 132 and second valve136. Process gas species and gas flow rates delivered into the processvolume 101 can be independently controllable. For example, gas flowthrough the upper gas injectors 130 may be different from gas flowthrough the lower gas injectors 134. The controller 126 governs thearray of valves 140.

In one embodiment, one or more inert gases, such as helium (He), argon(Ar) (or other inert gas), and/or one or more reactive gases, such ashydrogen (H₂), hydrogen bromide (HBr), ammonia (NH₃), disilane (Si₂H₆),methane (CH₄), acetylene (C₂H₂), nitrogen trifluoride (NF₃),tetrafluoromethane (CF₄), sulfur hexafluoride (SFs), carbon monoxide(CO), carbonyl sulfide (COS), trifluoromethane (CHF₃),hexafluorobutadiene (C₄Fe), chlorine (Cl₂), nitrogen (N₂), oxygen (O₂),combinations thereof, and the like can be supplied into the processvolume 101 through either or both the upper gas injectors 130 and thelower gas injectors 134. In some embodiments, the process gas deliveredto the process volume 101 adjacent the electrode 108 can acceleratesecondary electrons toward the substrate 111, as will be described ingreater detail below, and/or buffer the electrode 108 from a reactiveplasma formed in the process volume 101, thus increasing the useful lifeof the electrode 108.

In accordance with the present disclosure, plasma is generated in theprocess volume 101 by various bulk and surface processes, for example,by capacitive coupling 170 (e.g., capacitive coupling plasma (CCP))and/or inductive coupling 172 (e.g., inductive coupling plasma (ICP)).Inductively coupled power or high frequency capacitively coupled powercan be used to achieve independent control of plasma density, aside frombias power controlling ion energy. Accordingly, when the process chamber100 is configured for use with the capacitive coupling 170 (e.g.,configured as a CCP reactor), source power can refer to a higherfrequency (compared to bias) power being applied to either a biaselectrode (e.g., the electrode 144), which supports the substrate 111,or the upper electrode, e.g., the electrode 108. Alternatively oradditionally, when the process chamber 100 is configured for use withthe inductive coupling 172 (e.g., configured as an ICP reactor), thesource power refers to power applied to a coil 173 (shown in phantom inFIG. 1). When the process chamber 100 is configured as an ICP reactor, adielectric window 175 (also shown in phantom) is provided on a side ofthe chamber body 102 of the process chamber 100. The dielectric window175 is configured to provide a vacuum boundary and a window forelectromagnetic wave exciting plasma.

The inventors have found that ions generated by a CCP or ICP areinfluenced by an electric field that encourages ion bombardment of theelectrode 108 by the ions generated from the plasma, as will bedescribed in greater detail below. Moreover, depending on a mode ofoperation of the process chamber 100, ion bombardment energy of theelectrode 108 can be a function of a power supplied to the electrode108, e.g., provided by one or more of the DC voltage power supply 154,the low frequency RF power generator 122, or the high frequency RF powergenerator 120. For example, in at least some embodiments, ionbombardment energy of the electrode 108 can be provided by applicationof voltage from one or both the DC voltage power supply 154 and the lowfrequency RF power generator 122. In at least some embodiments, inaddition to using one or both the DC voltage power supply 154 and thelow frequency RF power generator 122, the high frequency RF powergenerator 120 can be used to increase plasma density and ebeam flux.

When the DC voltage power supply 154 is used to supply power (e.g.,bias) to the electrode 108, the power supplied by the DC voltage powersupply 154 can be about 1 W to about 30 kW (e.g., about −1560V to about−1440V). Similarly, when the low frequency RF power generator 122 isused to supply power (e.g., bias) to the electrode 108, the powersupplied by the low frequency RF power generator 122 can be about 1 W toabout 30 KW with a frequency from about 100 kHz and about 20 MHz.Likewise, when the high frequency RF power generator 120 is used inconjunction with either or both the DC voltage power supply 154 and thelow frequency RF power generator 122, the power supplied by the highfrequency RF power generator 120 can be about 1 W to about 10 kW with afrequency from about 20 MHz and about 200 MHz.

The ion bombardment energy of the electrode 108 and the plasma densitycan be functions of both the high frequency RF power generator 120 andthe low frequency RF power generator 122 and the DC voltage power supply154. For example, in at least some embodiments, the ion bombardmentenergy of the electrode 108 is substantially controlled by the lowerfrequency power from the low frequency RF power generator 122 (or the DCvoltage power supply 154) and the plasma density in the process volume101 can be substantially controlled (enhanced) by the power from thehigh frequency RF power generator 120. In at least some embodiments, ionbombardment of the electrode 108 causes the electrode 108 to emitsecondary electrons. Energetic secondary electrons, which have anegative charge, are emitted from the interior surface of the electrode108 and accelerated away from the electrode 108 due to the negative biasof the electrode 108, as will be described in greater detail below.Additionally, to increase ebeam bombardment dose at a substrate surface,a relative power provided by each of the low frequency RF powergenerator 122 and/or the DC voltage power supply 154 can be varied tovary a corresponding voltage provided at the electrode 108 and/or theelectrode 144, as will be described in greater detail below.

An ebeam flux of energetic electrons from the emitting surface of theelectrode 108 may be oriented substantially perpendicular to theinterior surface of the electrode 108. A beam energy of the ebeam can beapproximately equal to the ion bombardment energy of the electrode 108,which typically can range from about 100 eV to 20,000 eV. At least aportion of the ebeam, comprised of the secondary electron flux emittedfrom electrode 108 due to energetic ion bombardment of the electrode 108surface, propagates through the process volume 101 and reacts withprocess gases near the substrate 111. With utilization of the one ormore previously described process gases, such as Ar, the inventors havefound that the effect of ebeam bombardment on the substrate 111 can usedin a variety of ways. First, as noted above, the inventors have foundthat ebeam bombard on a reactive species adsorbed surface can induceetching reactions (e.g., EBIE), which provides damage free etch and highetch selectivity to a substrate.

Second, as an electric field on a surface of a substrate is alwayspointing towards the substrate, charging effects can negatively affectthe processing of a substrate. More particularly, electrons can onlyapproach a substrate during a moment of sheath (e.g., electrostaticsheath) collapse, e.g., at a positive peak of an RF cycle, for chargeneutralization. Additionally, with increasing aspect ratio, less andless electrons from bulk plasma can reach a bottom of etching features.Therefore, positive charges can accumulate at the bottom of etchingfeature and build up an electric field that retards incoming ions. Forexample, based on empirical data, for a memory hole with aspect ratio of50:1, more than fifty percent of ions cannot reach the bottom of thememory hole and there is a significant reduction in ion energy due topositive field retardation. The charging effect, together with neutraltransportation limitation, can cause a slow-down in etch rate withincreasing aspect ratio (e.g., ARDE effect). Furthermore, the chargingeffect can cause deflection of ion trajectory (e.g., ion bombardment onsidewall instead of vertically downwards), thus causing challenges inetch profile control such as bowing, twisting, under-etch andmicro-trenching. Accordingly, the inventors have found that ebeambombard can be used to neutralize the positive ion charges accumulatedat a bottom and/or a sidewall of etch features (e.g., memory holes),thus eliminating charging effects.

In some embodiments, an RF bias power generator 162 can be coupledthrough an impedance match 164 to an electrode 144 of the pedestal 110.The RF bias power generator 162, if used, is configured to accelerateions onto the substrate 111. The RF bias power generator 162 can beconfigured to provide low frequency RF power and/or high frequency RFpower. For example, in at least some embodiments, the RF bias powergenerator 162 can be configured to supply 1 W to 30 kW of power to theelectrode 144 at one or more frequencies, e.g., of about 100 kHz toabout 200 MHz. In some embodiments, for example, the RF bias powergenerator 162 can be configured to supply 1 W to 30 kW of power to theelectrode 144 at a frequency of about 100 kHz to about 100 MHz.

A waveform tailoring processor 147 may be connected between an output ofthe impedance match 164 and the electrode 144 and/or an output of theimpedance match circuit 124 and the electrode 108. The waveformtailoring processor 147 controller can be configured to change awaveform produced by the RF bias power generator 162 and/or the highfrequency RF power generator 120 and the low frequency RF powergenerator 122 to a desired waveform. The ion energy of plasma near thesubstrate 111 and/or the electrode 108 can be controlled by the waveformtailoring processor 147. For example, in some embodiments, the waveformtailoring processor 247 produces a waveform in which an amplitude isheld during a certain portion of each RF cycle at a level correspondingto a desired ion energy level. The controller 126 controls the waveformtailoring processor 147.

Etching of the substrate 111 can be also influenced by one or morefactors. For example, pressure (in addition to ebeam energy, ebeamplasma power, and bias power if used) can influence etching of thesubstrate 111. Accordingly, in an embodiment, a pressure maintained inthe process volume 101 during EBIE of the substrate 111 can be betweenabout 0.1 mTorr to about 300 mTorr. For example, in at least someembodiments, such as when ebeam neutralization and etch profile controlare necessary, a pressure maintained in the process volume 101 duringEBIE of the substrate 111 can be between about 0.1 mTorr to about 30mTorr. Likewise, in at least some embodiments, such as when ebeamneutralization and etch profile control are not necessary and bias poweris not needed, a pressure maintained in the process volume 101 duringEBIE of the substrate 111 can be between about 0.1 mTorr to about 100mTorr. The pressure is generated by a vacuum pump 168 which is in fluidcommunication with the process volume 101. The pressure is regulated bya gate valve 166 which is disposed between the process volume 101 andthe vacuum pump 168. The controller 126 controls the vacuum pump 168and/or the gate valve 166.

FIG. 2 is a flowchart of a method 200 for processing a substrate, inaccordance with one or more embodiments of the present disclosure. Themethod 200 can be performed using, for example, a process chamber thatis configured for performing EBIE of a substrate, e.g., the processchamber 100. For illustrative purposes, the process chamber is assumedconfigured as a CCP reactor configured for EBIE of a substrate, e.g.,the substrate 111, which can be, for example, a 150 mm, 200 mm, 300 mm,450 mm substrate, etc. For example, in at least some embodiments, thesubstrate can be a 300 mm substrate, such as a semiconductor wafer orthe like. As can be appreciated, the herein described power/voltagesand/or pulsing/duty cycles can be scaled accordingly, e.g., forsubstrates having diameters greater or less than 300 mm. Initially, oneor more of the above described process gases can be introduced into aprocess volume, e.g., the process volume 101, of the process chamber.For example, in at least some embodiments, the process gas can be one ormore of He, Ar, and the like (or other inert gas), and/or H₂, HBr, NH₃,Si₂H₆, CH₄, C₂H₂, NF₃, CF₄, SF₆, CO, COS, CHF₃, C₄F₆, Cl₂, N₂, O₂, andthe like (or other reactive gas). Additionally, the process volume canbe maintained at one or more operating pressures from about 0.1 mTorr toabout 300 mTorr. For example, in at least some embodiments, the pressurecan be maintained at 0.1 mTorr to about 100 mTorr.

At 202, one or both of low frequency RF power and DC power can beapplied to an upper electrode (e.g., the electrode 108), which, as notedabove, can be formed from a high secondary electron emission coefficientmaterial, disposed adjacent to the process volume. For example, in atleast some embodiments, an RF power generator, e.g., the low frequencyRF power generator 122, can be used to supply low frequency RF power tothe upper electrode. As noted above, the low frequency RF power appliedto the upper electrode can be about 1 W to about 30 KW and can beprovided at a frequency of about 100 kHz to about 20 MHz.

Alternatively or additionally, at 202, DC power, e.g., using the DCvoltage power supply 154, can be supplied to the upper electrode. Forexample, DC power of up to about 20 kW (e.g., corresponding to about 0to about 20 kV of supply voltage) can be provided. The inventors havefound that using DC power at 202 results in forming a narrow ebeam e.g.,narrow electron energy distribution.

In at least some embodiments, at 202, in conjunction with the lowfrequency RF power and/or the DC power, high frequency RF power can alsobe supplied to the upper electrode using, for example, a high frequencyRF power generator, e.g., the high frequency RF power generator 120. Asnoted above, the high frequency RF power can be used to increase plasmadensity or ebeam flux.

Next 204, a plasma comprising ions can be generated in the processvolume using, for example, the power provided to the upper electrode.For example, the process gas introduced into the process volume can beignited using the DC power, the low frequency RF power, and/or the highfrequency RF power provided to the upper electrode to create the plasma.

Next, at 206, the upper electrode is bombarded with the ions to causethe upper electrode to emit secondary electrons and form an ebeam. Moreparticularly, the low frequency RF power (or the DC power) at the upperelectrode is used to produce a high sheath voltage, so that ionbombardment (e.g., using ions formed from the plasma) on the upperelectrode is energetic enough to release secondary electrons from theupper electrode. In some embodiments and as noted above with respect to202, high frequency RF power can also be applied to the upper electrodeto increase plasma density or ebeam flux.

At 208, a bias power is supplied to a lower electrode (e.g., theelectrode 144). For example, in at least some embodiments, the biaspower can be supplied to the lower electrode using an RF bias powergenerator, e.g., the RF bias power generator 162, that is configured tosupply either low frequency RF power or high frequency RF power to thelower electrode for accelerating electrons of the ebeam toward the lowerelectrode. More particularly, the high sheath voltage at the upperelectrode and the relatively low bias potential at the lower electrodeaccelerates the secondary electrons into the main plasma with enoughenergy to overcome the substrate sheath potential and reach a substratesurface (e.g., the substrate 111).

In at least some embodiments, one or more gases can be used to enhanceheat transfer from the pedestal (and/or the lower electrode) to thesubstrate. For example, in at least some embodiments, He or othersuitable gas for transferring heat can be applied, using, for example,one or more gas supplies (e.g., gas supplies 138), between the pedestal(and/or the lower electrode) and the substrate to enhance heat transfer.

The generated ebeam can be used to etch the substrate to form one ormore features on the substrate. For example, in some embodiments, thegenerated ebeam can be used to form one or more memory holes in thesubstrate. More particularly, the inventors have found that the ebeamcan be used to form memory holes with an etch depth of about 200 nm toabout 500 nm, with no ARDE effect, no bowing or twisting of thesidewalls that define the memory hole, and with better CD (e.g., flatbottom) and relatively straight profiles.

The inventors have also found that one or more pulsing schemes (e.g.,control of pulsing duty cycle, pulsing synchronization, duty cycle anddelay) can be used to control a balance between ebeam flux and ion flux.For example, in the method 200, any supplied RF power can use a pulsingor continuous wave (CW) mode to achieve desired results for differentapplications (e.g., high or low aspect ratio, logic or memory, etc.).Alternatively or in combination, in the method 200, any supplied DCpower can use a pulsing or continuous mode to achieve desired resultsfor different applications (e.g., high or low aspect ratio, logic ormemory, etc.). More particularly, to maximize ebeam bombardment doseincident on the substrate, one or more pulsing schemes can be used asdescribed below.

In at least some embodiments, for example, one or both of low frequencyRF power or DC power can be continuously provided to the upper electrode(as described above with respect to 202) and low frequency RF power canbe provided to the lower electrode (as described above with respect to208). In some embodiments, the DC power supply voltage provided to theupper electrode is greater than the low frequency RF power supplyvoltage provided to the lower electrode during at least some portion ofthe sinusoidal cycle of the low frequency RF power. In addition, in someembodiments, the low frequency RF power supply voltage provided to thelower electrode can be pulsed at a low duty cycle (e.g., about tenpercent (10%) to about seventy percent (70%), such as about fiftypercent (50%)). The pulse frequency can be from about 50 Hz to about 100kHz. Using such a pulsing scheme reduces substrate sheath potential(e.g., during the low frequency RF power off time at the lowerelectrode), thus increasing ebeam bombardment dose at the substratesurface. That is, only ebeam electrons with energy higher than asubstrate sheath potential can reach the substrate surface.

In embodiments when low frequency RF power is supplied to the upperelectrode, pulsing can be configured such that when power is supplied tothe upper electrode, low frequency RF power is not supplied to the lowerelectrode, and vice versa. Alternatively, the low frequency RF power canbe supplied in CW mode to the upper electrode and low frequency RF powercan be supplied to the lower electrode in a pulsed low duty cycle, asdescribed above.

In at least some embodiments, both low frequency RF power and DC powercan be supplied to the upper electrode and lower electrode in a pulsingmode, but synchronized in such a way that when power is supplied to theupper electrode, power to the lower electrode is off. For example, whenone or both of low frequency RF power and DC power is supplied to theupper electrode, low frequency RF power is not supplied to the lowerelectrode. In such an embodiment, the on/off pulsing cycles can be setat a frequency of about 100 Hz to about 100 kHz. In such an embodiment,alternate ion fluxes and ebeam fluxes are applied to the substrate, thusincreasing ebeam bombardment dose at the substrate surface.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof.

1. An apparatus for processing a substrate, comprising: a controllerconfigured to: apply at least one of low frequency RF power or DC powerto an upper electrode formed from a high secondary electron emissioncoefficient material disposed adjacent to a process volume; generate aplasma comprising ions in the process volume; bombard the upperelectrode with the ions to cause the upper electrode to emit electronsand form an electron beam; apply a bias power comprising at least one oflow frequency RF power or high frequency RF power to a lower electrodedisposed in the process volume to accelerate electrons of the electronbeam toward the lower electrode; apply the at least one of low frequencyRF power or DC power in a continuous mode to the upper electrode; andwhen the bias power comprises low frequency RF power, apply the lowfrequency RF power to the lower electrode in a pulsing mode, such that agiven pulse of low frequency RF power provides a voltage to the lowerelectrode that is less than a voltage applied to the upper electrodeduring at least some portion of a sinusoidal cycle of the low frequencyRF power.
 2. The apparatus of claim 1, wherein the high secondaryelectron emission coefficient material is at least one of silicon (Si),silicon nitride (SiN), silicon oxide (SiO_(x)), or carbon (C).
 3. Theapparatus of claim 1, wherein the plasma comprising the electronscomprises at least one of helium (He), argon (Ar), hydrogen (H₂),hydrogen bromide (HBr), ammonia (NH₃), disilane (Si₂H₆), methane (CH₄),acetylene (C₂H₂), nitrogen trifluoride (NF₃), tetrafluoromethane (CF₄),sulfur hexafluoride (SF₆), carbon monoxide (CO), carbonyl sulfide (COS),trifluoromethane (CHF₃), hexafluorobutadiene (C₄F₆), chlorine (Cl₂),nitrogen (N₂), or oxygen (O₂) into the process volume.
 4. The apparatusof claim 1, wherein the controller is further configured to maintain theupper electrode from a process position for processing a substrate at adistance of about 1 inch to about 20 inches.
 5. The apparatus of claim1, wherein the controller is further configured to maintain a pressurewithin the process volume from about 0.1 mTorr to about 300 mTorr. 6.The apparatus of claim 1, wherein the controller is further configuredto apply high frequency RF power in conjunction with the at least one oflow frequency RF power or DC power to the upper electrode.
 7. Theapparatus of claim 1, wherein when the bias power comprises lowfrequency RF power, the controller is further configured to apply thelow frequency RF power to the lower electrode in the pulsing mode, suchthat when the at least one of low frequency RF power or DC power to theupper electrode is pulsed on, the low frequency RF power to the lowerelectrode is pulsed off.
 8. The apparatus of claim 1, wherein the lowfrequency RF power provided to the lower electrode can be pulsed at alow duty cycle.
 9. The apparatus of claim 8, wherein the low duty cycleis about ten percent to about seventy percent.
 10. The apparatus ofclaim 8, wherein low duty cycle is about fifty percent.
 11. Theapparatus of claim 8, wherein a pulse frequency is about 50 Hz to about100 kHz.